With the increase of the operation speed of analog circuits, minute components are often used in a semiconductor chip. However, the minute components have a problem that the fluctuation of its performance is large. Because this fluctuation influences the yield of the semiconductor chip, it is desired to improve the yield by conducting appropriate design of the semiconductor chip in addition to improvement of the manufacturing process. However, typically, because there is an antinomy between the yield and the performance, it is preferable that the circuit design is carried out while appropriately evaluating the yield and performance.
On the other hand, as for methods for conducting automatic circuit design, multiobjective optimization and single objective optimization are used. The multiobjective optimization is a method for calculating a set (i.e. pareto curve or surface in a solution space) of solutions (i.e. non-dominated solution) that is not dominated by other solutions in the solution space. The pareto curve or surface will be explained in detail later. On the other hand, the single objective optimization is a method for searching the design space for a point whose value of a predetermined evaluation function becomes minimum. In the single objective optimization, when any solution to realize the requirement specification cannot be obtained, the optimization processing is carried out again after changing the requirement specification. Hence, the efficiency is poor. In addition, when an initial value is not proper, a lot of searches in the design space are carried out in the single objective optimization. On the other hand, the processing amount of the multiobjective optimization typically becomes large because a set of non-dominated solutions is calculated. However, once the non-dominated solutions are generated, the processing amount after that becomes little. This is an advantage.
Incidentally, an example that the multiobjective optimization is applied to the design of the analog circuits already exists. In addition, a conventional art that the yield is considered also exists, and in this conventional art, by fixing the influence of PVT (i.e. Process, Voltage and Temperature) variations to the performance, the fixed yield rate is assumed as depicted in FIG. 1, and the pareto curve at that time is generated. FIG. 1 depicts pareto curves for the yields 20%, 50% and 80% in the performance space of the performances frequency bandwidth and gain, and the pareto curves are calculated while fixing the yield rates. In such a method, because the respective rates are individually set to generate the pareto curves, the efficiency of the processing is poor. In addition, because the pareto curve is generated for each yield rate, any relationship between the yield and performance for each design.
In other words, it is impossible for the conventional arts to appropriately evaluate the relationship between the yield and performance.